1. Technical Field
The present invention relates to a sensor for detecting compounds. More specifically, the present invention relates to a sol-gel sensor capable of a color change via a charge-transfer mechanism upon detection of a chemical and surface contaminant.
2. Description of Related Art
A major goal of analyte detection research is to develop inexpensive, fast, reliable, and sensitive detectors. Unfortunately, the technologies developed to date have only met some of these goals, and no single device has sufficiently attained a majority of them.
Classical detection methods such as liquid chromatography (LC), gas chromatography (GC), and supercritical fluid chromatography (SFC), in combination with mass spectrometry, are widely used and provide accurate identification of analytes and quantitative data. However, these techniques are time consuming, extremely expensive, require sample preconcentration, and are difficult or impossible to adapt to field use.
Biosensors (i.e., devices containing biological material linked to a transducing apparatus) have been developed to overcome some of the shortcomings of the classical analyte detection techniques. Many currently used biosensors are associated with transducer devices that use photometry, fluorimetry, and chemiluminescence; fiber optics and direct optical sensing (e.g., grating coupler); surface plasmon resonance; potentiometric and amperometric electrodes; field effect transistors; piezoelectric sensing; and surface acoustic wave (Kramer, J. AOAC Intern. 79: 1245 [1996]). However, there are major drawbacks to these devices, including dependence on a transducing device that prevents miniaturization and requires a power source. These disadvantages make such devices too complex, expensive, or unmanageable for routine analyte detection applications such as for field work or home use. Additionally, many of these devices are limited by the lack of stability and availability of the biological materials (e.g., proteins, antibodies, cells, and organelles).
Immunoassay methods can also be used for detecting certain types of analytes. In immunoassays, antibodies are developed to specifically bind to a target of interest (e.g., an analyte). By labeling the antibody (e.g., with dye or fluorescent or radioactive material), binding of the antibody to an analyte can be detected. However, immunoassay methods have limited use because they require production of antibodies against each analyte of interest. Antibodies cannot be generated against some types of analytes. Additionally, the generation of antibodies can be time consuming, expensive, and extremely difficult.
Most agricultural pesticides (APs), insecticides, and chemical warfare agents (CWAs) are organophosphorus esters that can irreversibly react with the enzyme acetyl cholinesterase, thereby inhibiting its control over the central nervous system. FIG. 1 illustrates the structure of four major CWAs and three commonly used APs.
The detection and decontamination of these highly toxic agents in production sites, stockpiles, and application (or contaminated) fields (agricultural fields and battlefields) are labor-, material-, and time-intensive using current methodologies. An indicator is needed to reduce the burden of determining what pieces of equipment are contaminated and decontaminating every piece of equipment and personnel from a suspected contaminated environment. Such a decontamination indicator should be easy to use, cost-effective, and compatible with all operational equipment. A colorimetric indicator is preferred.
Currently, no effective colorimetric indicators are available for the on-site sensing of APs and CWAs. The current on-site method for the detection of these highly toxic and deadly agents in aqueous samples uses a methylene chloride extraction, followed by a concentration step or solid-phase extraction/elution and derivatization. The samples are then analyzed by gas chromatography-mass spectrometry (GC-MS). The sample preparation and analysis are time consuming. One focus of current research is to develop fast on-site screening methods that require less sample preparation. Among the options being explored are ion-chromatography, micro high-performance liquid chromatography, micellar electrokinetic chromatography, and capillary electrophoresis. However, to date, no effective detector/indicator has been developed that is capable of being affixed to a surface.
The previously developed detection methods for CWAs are M8/M9 paper and chemical agent monitor (CAM). The paper type of chemical detector generally shows a light color change upon some chemical reactions between contaminants and color indicator on the paper (M8/M9 paper). Generally, a reasonable amount of reactive chemical agents are needed to wet the active area of the paper, and then to promote and observable color change. It is difficult to collect free liquid agent from a coarse adsorbing surface such as, fabric, soil, concrete, or on moving vehicles.
There remains a need for analyte detectors and decontaminators that provide the specificity of biosensors and the benefit of calorimetric sensors, but also provide the cost-efficiency, stability, accuracy, reliability, reproducibility, and robustness that is lacking from available technologies. In particular, development of devices that can be miniaturized with controlled shapes and that do not rely on an energy source and can be coated on a predetermined surface would also be very beneficial, particularly for routine fieldwork and home use.